One thing I was trying to do when making Medical Bay Three was to make it a game where the player didn’t have to know anything about being a doctor to play a doctor in the game. Everything you need to know is on the patient’s chart: it lists a variety of diseases common to that alien species, and connects them to symptoms. But most symptoms connect to multiple diseases, so you have to investigate and rule out possibilities and try stuff to figure out what is actually going on.
This is largely inspired by the brilliant Quade diagram used in Robin Laws’s underrated game Mutant City Blues. In that game, you’re cops in a world full of X-men style mutants. So to solve a crime, you have to know a lot about how superpowers work in the setting. And the game externalizes that into the Quade diagram, which connects superpowers (and a few other details about the mutant) in a systematic way. So a superpower might be linked to genetic albinoism. So if you find evidence of that superpower in a crime scene, then you start looking for albinos in the supporting cast, as they’re more likely to be the culprit. Or if you see evidence of two powers on the opposite sides of the diagram, you’re more likely dealing with two perps than one.
Both of these diagrams let the player explore a series of interconnected abstract ideas, and make meaningful decisions about them, all in a controlled fashion. For Medical Bay Three, my players were looking at symptoms and identifying them and crossing them off and trying to isolate the disease’s cause to specific parts of the chart. The organizations meant that they could make meaningful, informed decisions about the subject matter. If they hadn’t had the chart, the information would have been loose and harder for them to integrate into knowledge that they could use to make meaningful decisions.
By ‘meaningful decisions’ I mean that the player has a choice that they can make, which has observable consequences and that they can predict some (but not necessarily all) of the consequences of the decisions. Ideally, your game provides the player with meaningful decisions rather than meaningless ones. (A meaningless decision would either have no notable consequences, or the consequences are completely unknowable. These aren’t really fun to have in play.)
Relationship maps can facilitate meaningful decisions as well, letting a player know at a glance how PCs and NPCs relate to one another and therefore what the consequences of an interpersonal interaction might be. Neel Krishnaswami (one of the smartest guys I’ve ever gamed with) wrote a really good article a decade ago about using causality diagrams to model science fiction technology. (See it here: web.archive.org/web/20040715080350/http://www.chimera.info/daedalus/downloads/daedalus-winter2004.pdf#86 ) I’ve used that technique in the past in larps to let people interact with and sabotage science fiction technologies with semi-predictable results. Once again, these diagrams clarify the cause and effect relationships in a system so that the player can (at least partially) predict outcomes of their decisions. The diagrams help the player make meaningful decisions.
Ultimately, well designed dungeons work like this as well. The idea of a dungeon, after all, is to take this whole complicated, messy fantasy genre and condense it down to a series of concrete, discrete and meaningful decisions. Do you sneak past the goblin guards (and risk being surrounded on all sides when the alarm is raised) or do you kill them (and risk the noise of battle alerting the other monsters)? Do you head down the stairs covered in slime (which suggests a nasty tentacled monster below) or into the hall full of statues (Medusa? Gargoyles? Basilisk? Golems?)? Do you keep pressing into the dungeon, or retreat to camp outside or risk camping out inside an apparently safe room? The dungeon setup of corridors and rooms and monster encounters and such allows the player to make meaningful decisions about exploration and logistics and such. (This is, incidentally, why I think dungeon crawls are better if the PCs get a map of the dungeon ahead of time. Preferably an incomplete or untrustworthy map. More meaningful decisions that way.) Battlemats do the same for combat situations: the idea is to make the amorphous, ambiguous imaginary fight scene into a place where players can make meaningful decisions about positioning and tactics.
Having a diagram lets you make similar sorts of decisions, but about less concrete matters. A diagram might link together symptoms and diseases, or clues relating to the perpetrator, or how a machine operates, or any number of other bits of knowledge. And by laying it out there in front of the players, they can take those connections and relations and make more meaningful decisions about it.